How does electric power
production use and consume water?

Cooling Technologies
Thermal electric generating facilities make electricity by converting
water into high-pressure steam that drives turbines. Once water has gone
through this cycle, it is cooled and condensed back to water and then
reheated to drive the turbines again. The process of condensation requires
a separate cooling water body to absorb the heat of the steam. These condenser
systems typically consist of banks of thousands of one-inch diameter tubes,
through which cooling water is run, and over which the hot steam and water
is circulated.

Two cooling technologies
are in use today:

Closed-cycle
systems discharge heat through evaporation in cooling towers and recycle
water within the power plant. The water required to do this is comparatively
small since it is limited to the amount lost through the evaporative
process. Because of the expense associated with closed-cycle cooling,
once-through systems are far more common.

Once-through
systems require the intake of a continual flow of cooling water. The
water demand for the once-through system is 30 to 50 times that of a
closed cycle system.

The amount of water
used for power plant cooling also varies by each specific power plant's
electricity generating technology and size. For example, nuclear reactors
require the most water for cooling, and baseload fossil fuel power plants
come in second. Steam electric generating plants across the nation draw
in more than 200 billion gallons per day. Most renewable energy technologies
require little or no water for cooling.

Hydropower Generation
To generate
power, hydropower plants divert water from the river through turbines.
Water is diverted from the river via an intake at the dam. At some hydropower
plants, the turbines are located in the dam and thus the water is released
again right below the dam. At other hydropower plants, the turbines are located
in a powerhouse significantly downstream from the dam (in order to generate
enough height difference, or "head," between where the water is diverted
to where the power is generated). This means that the water can be diverted
outside of the stream for some distances, sometimes several miles, before
being released back in the river.

What do we mean by water
use and consumption?

Most electric power
plants require water to operate. Nuclear and fossil fuel power plants
drink over 185 billion gallons of water per day. Geothermal power plants
add another 2 billion or so gallons a day. Hydropower plants use water
directly to generate power. These power plants represent the single largest
consumer of water among any industrial, governmental or residential activity.
Since 98 percent of the water used in power plants is returned to its
source, distinctions are made between use and consumption.

Water use
is a measure of the amount of water that is withdrawn from an adjacent
water body (lakes, streams, rivers, estuaries, etc.), passes through various
components of a power plant, and is then ultimately discharged back into
the original water body. Environmental concerns surrounding water use
center around any chemical or physical alteration of the water body and
any impacts these changes may have on the plants, fish and animals who
reside in the ecosystem.

Water consumption
refers to water sucked up in power plant operations that is lost, typically
through evaporation. The primary concerns surrounding water consumption
is how best to utilize this essential resource, especially in areas, such
as deserts in the West, where water is in short supply.

What are the consequences of water use and consumption?

Withdrawal of large
volumes of surface water for either power plant cooling or hydropower
generation can kill fish, larvae and other organisms trapped against intake
structures (impinged), or swept up (entrained) in the flow
through the different sections of a power plant.

Large fossil fuel
and nuclear plants require incredible quantities of water for cooling
and ongoing maintenance. The Salem Nuclear Generating Station alone takes
3 billion gallons a day from the Delaware Bay. Studies of the environmental
consequences of this phenomenal water demand indicates that Salem is responsible
for an annual 11 percent reduction in weakfish and 31 percent reduction
in bay anchovy. At
the Indian Point 2 and 3 reactors on the Hudson River, the number of fish
impinged totaled over 1.5 million fish in 1987. The 90 power plants using
once-through-cooling (see below) on the Great Lakes kill in excess
of 40 million fish per year due to impingement (Pace University, Environmental
Costs of Electricity, p. 287).

The use of water
to generate power at hydropower facilities imposes unique, and by no means
insignificant, ecological impacts. The diversion of water out of the river
removes water for healthy in-stream ecosystems. Stretches below dams are
often completely de-watered. Fluctuations in water flow from peaking operations
create a "tidal effect," disrupting the downstream riparian community
that supports its unique ecosystem. A dam's impoundment slows water flows,
which hinders natural downstream migration of many fish species. By slowing
river flows, dams also allow silt to collect on river and reservoir bottoms
and bury fish spawning habitat. Silt trapped above dams accumulates heavy
metals and other pollutants. Disrupting the natural flow of sediments
in rivers also leads to erosion of riverbeds downstream of the dam and
increases risks of floods.

The impoundment of
water by hydropower facilities fundamentally reshapes the physical habitat
from a riverine to an artificial pond community. This often eliminates
native populations of fish and other wildlife. Dams also impede the upstream
and downstream movement of fish and other wildlife, and prevent the flow
of plants and nutrients. This impact is most significant on migratory
fish, which are born in the river and must migrate downstream early in
life to the ocean and then migrate upstream again to lay their eggs (or
"spawn"). As mentioned above, withdrawal of water into turbines can also
impinge or entrain significant numbers of fish.

How can consumer electricity choice address water use and consumption?

By re-directing their
electricity dollars to support environmentally benign energy resources,
consumers are empowered, in states that offer supply choice, to influence
the existing generating resources that are deployed to meet demand. They
can also support the construction of new and cleaner electricity resources
that will be built to meet overall growth in demand in the future. By
supporting these power options, consumers can minimize many water use
and consumption impacts. Still, it should be noted that directing one's
dollars to cleaner power products in no way helps remediate damages that
already have occurred. Consumers can stop the construction of new hydropower
facilities or alter conditions of siting and operation, but they cannot
undo previous environmental degradation that occurred at existing hydropower
facilities.

References:

The Energy Project, Land and Water Fund of the Rockies, How
the West Can Win: A Blueprint for a Clean and Affordable Energy Future
(1996).